Extraction of uranyl nitrate from aqueous solutions



2,8 16,005 Patented Dec. 10, 1957 EXTRACTION OF URANYL NITRATE'FROM AQUEOUS SOLUTIONS No Drawing. Application June 14, 1948,

' Serial No. 32,994

17 Claims. (Cl. 23-14.5)

This invention relates to compounds'of uranium and more particularly it relates to a method of extracting uranyl nitrate from an aqueous solution containing the same.

Heretofore the purification of uranium and compounds thereof has been a difficult and expensive process. One method of 'accomplishing such' a purification was to prepare an aqueous solution of uranyl nitrate and thereafter to extract the uranyl nitrate from the aqueous solution with diethyl ether. The distribution of uranyl nitrate between the ether and water layers is such that large volumes of the relatively expensive ether are required in order to recover the major portion of the uranyl nitrate even from saturated solution of the uranyl nitrate. Moreover, as the uranyl nitrate is extracted from the aqueous phase, the extraction efiiciency is reduced still further i until at a relatively high concentration a point is reached at which no appreciable aqueous layer.

The present invention provides an extremely eflicient and economical process for recovering substantially all of the uranyl nitrate present in an aqueous solution thereof. This process reduces materially the cost of extremely pure uranium and uranium compounds and makes possible quantities are removed from the large scale production thereof. Hence, the use of ura-...

mum-containing materials in ceramics and in metallurgical processes will be greatly benefited. Similarly, in the more recent use of uranium metal and compounds thereof in Various processes leading to the development of nuclear energy where materials of an extremely high degree of purity are required, the present process finds wide application.

Accordingly, it is an object of the present invention to provide an improved method of extracting uranyl nitrate from aqueous solutions thereof.

It is another object of the invention to improve the elficiency of extraction methods for uranyl nitrate from aqueous solutions.

It is a further object of the invention to improve the economy and efiiciency of the ether extraction of uranyl nitrate from aqueous solutions thereof.

Other objects will become apparent in the following description.

The present invention accomplishes the foregoing objects through the addition of at least one soluble nitrate salt to the aqueous solution of uranyl nitrate under such conditions that the product of the total nitrate ion normality of the solution and the distribution coeflicient exceeds a value of 20 and thereafter extracting'the uranyl nitrate from the solution with a selective organic solvent which is substantially immiscible with the uranyl nitrate solution. The distribution coeflicient is defined as the ratio of the concentration of uranyl nitrate in an organic solvent to the concentration in an aqueous solution at equilibrium with the organic solution.

The soluble nitrate salts that have been found most useful in this process are the nitrates of lithium, calcium,

pine, bivalent copper and trivalentiron. Sodium nitrate similarly has been used to some extent chiefly because of its cheapness. However, sodium nitrate is somewhat less satisfactory than the aforementioned nitrate salts since the distribution coefiicient of uranyl nitrate between diethyl ether and an aqueous solution of uranyl nitrate containing even large concentrations of sodium nitrate is relatively low when compared with the distribution c0- efiicients obtained in the presence of the othernitrate salts. For the most part,- the metal nitrate salts useful in attaining the objectives of the present invention are those which form well defined hydrates.

The principal selective organic solvent that has been used in accordance with the present method is diethyl ether although other immiscible solvents or mixtures of solvents may be used effectively provided they are solvents for uranyl nitrate.

In addition to the presence of the nitrate compounds which act as salting out agents it is preferable that the aqueous layer be slightly acid, that is, at a pH of 4 or less in order to attain complete extraction. The acidity of the solution is a relatively important factor since it prevents the hydrolysis of such salting out agents as ferric nitrate and in addition precludes the possibility of the formation of basic uranium salts. v

It appears that there is no appreciable distribution of uranyl nitrate from an aqueous layer into the selective organic solvent layerwuntil the total normality of the nitrate exceeds a value of about 2 or 3. The distribution increases rather rapidly after this point is reached especially in the presence of the nitrate ion and of the cations mentioned above which associate strongly with water.

Thus, ferric, calcium, 'cupric, zinc or lithium nitrate added to aqueous'ur anyl nitrate until the concentration of the nitrate ion in solution reaches the value of about 7 or 8 normal'will result in distribution coefficients between the organic and water layers of from 10 to times those observed with about 7 to 8 normal nitrate' solutions containingcertain other nitrates such as am-- monium nitrate.

In general, it is desirable that the present extraction process .be carried out under such conditions that the product of the distribution coefiicient and the total nitrate normality at equilibrium is at least 20. It has been found that exceptionally high values of this product, i. e., values ofthe orderof 500 to 3000 can be obtained by using as a salting out agent a nitrate selected from the group consisting of ferric, calcium,cupric, zinc and lithium nitrates. The examples following hereinafter are presented to illustrate the method of the present invention and it will be understood that the invention is not limited to the specific materials and conditions described therein.

Example 1 ,Calcium nitrate was added to a measured volume of 0.51 normal aqueous uranyl nitrate, increasing the total nitrate concentration to about 11.08 normal. This solution was shaken for about 15 minutes at 27.5 C. in a separatory funnel containing an approximately equal volume of diethyl ether so that an equilibrium distribu tion of uranyl nitrate was obtained between the aqueous and the ether phases. Theuranium in the water layer was separated from the calcium by precipitation as ammonium diuranate, and the uranium was determined volumetrically with ceric sulphate. Uranium in the. ether phase was estimated gravimetn'cally. The calcium concentration in the aqueous phase was determined by the. standard oxalate precipitation followed by permanganate titration. The distribution coefficient of uranyl nitrate, that is, the concentration in the etherphase divided by the concentration of the uranyl nitrate in the aqueous phase, was 165.4, and the product of the distribution coefiicient and the totalnitrate normality was 1836.

More than 99% of the uranyl nitrate in the aqueous phase was extracted by the ether.

In most cases where it is desirable to extract substantially all the uranyl nitrate from the aqueous solution thereof into the ether, it is advantageous to use relatively high i be mixed with a second solvent such as benzene or toluene and the mixtures used as extractants in accordance with the present invention. In general, it may be said, that the solvents most useful in carrying out the present inv H a vention are those in which not only the uranyl nitrate concentrati s 9 h s l flg g nt, preferably a subis soluble but also those in which water is slightly solusta-ntially saturated solution of the nitrate salt. The ble since it is indicated that the uranyl nitrateexists in reason for thisis that as the concentration of the salting the organic phase in a hydrated state, out agent decreases its etfect upon the distribution coefii- Many alternatives will be apparent to those killed in cient of the uranyl nitrate falls off rapidly as is shown in 10 the art. Tablel where calcium nitrate was employed as the salting Since many embodiments might be made 111 out agent. ent invention and since many changesmight be made in Ta the embodiment described, it is to be understood that the foregoing descriptionis to be interpreted as illustrative Product of only and not in a limiting sense.

Initial Aque- Total D istrlbu- Distribution V6 l i Normality oi ouslfhase Nitrate tion 09- Coeflicientand uyos), Normality r n -t ng efficient T m Nitrate 1. A method of extracting uranyl nitrate from an aqueous solution thereof which comprises dissolving in said i 1 solution c lcium. itrate to i crease the pr t o w10,57 M1 1108 16 L836 20 tot l.. ni rate i 11. fmrm ty d th distr utio 15.22 0:260 3.48 25. 1 213 cient to a value in excess of 20, and extracting uranyl {183 811 2 3; 81313 5; n trate-tram sai solut on-w h .a-se cctive organ solvent 11. obleith said sol tion- :By fo lowing. the .PrQGt-fidur? O tlined in Example 1 f g Qf gi g? i iif l with. fl QKC PtiQQ hat other nitrate salts .at concentrar spcufcmp 2 w comp/gigs said @095. Gloselo saturation were employed in the place of 9 ii i g net of tot?! calcium nitrate, the results shown. in Table 2 were obnmate 3 gonna the i coemcePt to tainei a value in excess of 20, and extracting uranyl nitrate Table 2 Product of Distribution I Initial Aque- Total Distribu- Coetfieient Ex. 'Salting Normalous Phase Nitrate tion (20- and Total No, Algent ityot Normality of Normality efiieient Nitrate Agent UOflNQg): Normalit at Equilibrlum Zn(N0i): 10. 88 0, 259 10. 9tv 2,57 2,810 comm); 9,33 1.98 11.31. 152.0 1,843 r 10.52 i 0.133 l 10.65 85.0 906 FGKNO)! 7.43 0.0 10 7.47 87.5 6.54

From the foregoing examples it becomes apparent that from said solution with a selective organic solvent immisit is highly advantageous to use calcium, zinc, copper, cible with said solution. lithium orfferric nitrate as the salting out agent; The 3. A method of extracting uranyl nitrate from an aqueaddition of nitrate-ion in the form Qt -ammonium nitrate ous solution thereof which comprises dissolving in said does not increase the distribution coefiicientof uranyl solution cupric nitrate to increase the product of the tonitrate between ether an'd an aqueous solution thereof 59 tal nitrate ion normality and the distribution coefl icient sufficiently. to make their use in the present-processcomto a value in excess of 20, andjextracting uranyl nitrate mercially. feasible. For example, when ammonium nifrom said solution with a selective organic solvent time is substituted for calcium nitrate in the procedure miscible with said solution. set forth in Example 1, the product of distribution co- 4. A method of extracting uranyl nitrate trornanaqueefiicient and totalnitrate normality is only about 14. ous solution thereof which comprises dissolving in said Nitric acid as a source oi nitrate ions for the present solution calcium nitrate .to increase the product of the purposes is not commercially feasible. total nitrateion normality and the distribution coeflicient Mixtures oi? salts may also be used in order to into a value in excess of 20, and extracting uranyl nitrate crease'the. distribution coeflicient of the uranyl nitrate. -from said solution with diethyl' ether.

When such mixtures are used, each of the nitrate salts 60 5. A method of extracting uranyl nitrate from an contributes-its efiect on the distribution coeflicient indeaqueous solution, thereof which comprises dissolving in pendently'oftheothers. The distribution coefficient obsaid solution cupri'cfnitrate to increase the product of tained depends upon the proportion of; the total nitrate the total nitrate ion normality and the distribution coion concentrationcontributed-by each salt and upon the eflici'ent .to a value in excess of 2.0, and extracting uranyl distribution coefficient which would; be obtained if each nitrate frorn said solufonwithdiethylether.

salt were present at a concentration equivalent to the 6. A method o ijextracting uranyl nitrate from an aquetotal concentration of all the nitrate salts actually presous solution thereof which comprises dissolving in said a l li i r m? nitrate inqe se hc p oduc f. he t In this process other organic solvents may be used for tall nitrate ion normality. and the distribution. eoetiicient the extraction of uranyl nitrate such as isopl'opyl and to a value in, excess of20, andextracting uranyl, nitrate benzylethers and ethyl acetate. Isopropyl. and normal from said solution with diethylether, said solution being propyl alcohol, normally completely miscible with water, maintained at a pH of; less than 4. may also be used since they are immisciblewith Saturated 7. A method of extracting uranyl nitrate from an aquesolutions of nitrate salts. The but ylialcohols may be ous solution thereof which comprises substantially. satuused in a manner similar to, the propyl alcohols. 891+ rat in g said solution with calcium nitrate to, increase the vents such as ethyl and methyl alcoholand acetone may product of the total nitrate ion normality and the distribution coefficient to a value in excess of 20, and extracting uranyl nitrate from said solution with a selective organic solvent immiscible with said solution.

8. A method of extracting uranyl nitrate from an aqueous solution thereof which comprises substantially saturating said solution with ferric nitrate to increase the product of the total nitrate ion normality and the distribution coefiicient to a value in excess of 20, and extracting uranyl nitrate from said solution with a selective organic solvent immiscible with said solution.

9. A method of extracting uranyl nitrate from an aqueous solution thereof which comprises substantially saturating said solution with cupric nitrate to increase the product of the total nitrate ion normality and the distribution coefficient to a value in excess of 20, and extracting uranyl nitrate from said solution with a selective organic solvent immiscible with said solution, said solution being maintained at a pH of less than 4.

10. A method of extracting uranyl nitrate from an aqueous solution thereof which comprises substantially saturating said solution with calcium nitrate to increase the product of the total nitrate ion normality and the distribution coefiicient to a value in excess of 20, and extracting uranyl nitrate from said solution with diethyl ether, said solution being maintained at a pH of less than 4.

11. A method of extracting uranyl nitrate from an aqueous solution thereof which comprises substantially saturating said solution with ferric nitrate to increase the product of the total nitrate ion normality and the distribution coeflicient to a value in excess of 20, and extracting uranyl nitrate from said solution with diethyl eflier.

12. A method of extracting uranyl nitrate from an aqueous solution thereof which comprises substantially saturating said solution with cupric nitrate to increase the product of the total nitrate ion normality and the distribution coefiicient to a value in excess of 20, and extracting uranyl nitrate from said solution with diethyl ether.

13. A process of extracting uranyl nitrate from an aqueous solution thereof which comprises dissolving in said solution at least one metal nitrate selected from the group consisting of the nitrates of lithium, calcium, bivalent copper, zinc and trivalent iron, and extracting uranyl nitrate from said solution with a selective solvent immiscible with said solution.

14. A process of extracting uranyl nitrate from an aqueous solution thereof which comprises dissolving in said solution a metal nitrate selected from the group consisting of the nitrates of lithium, calcium, bivalent copper, zinc and trivalent iron, and extracting uranyl nitrate from said solution with an ether.

15. A process of extracting uranyl nitrate from an aqueous solution thereof which comprises dissolving in said solution a metal nitrate selected from the group consisting of the nitrates of lithium, calcium, bivalent copper, zinc and trivalent iron, and extracting uranyl nitrate from said solution with diethyl ether.

16. A process of extracting uranyl nitrate from an aqueous solution thereof which comprises substantially saturating said solution with a metal nitrate selected from the group consisting of the nitrates of lithium, calcium, bivalent copper, zinc and trivalent iron, and extracting uranyl nitrate from said solution with an ether.

17. A process of extracting uranyl nitrate from an aqueous solution thereof which comprises substantially saturating said solution with a metal nitrate selected from the group consisting of the nitrates of lithium, calcium, bivalent copper, zinc and trivalent iron, and extracting uranyl nitrate from said solution with a selective solvent immiscible with said solution, said solvent comprising an organic alcohol having less than 5 carbon atoms.

Misciattelli, Gazzetta Chimica Italiana, vol. 66, pp. 833-838 (1930). 

13. A PROCESS OF EXTRACTING URANYLNITRATE FROM AN AQUEOUS SLOUTION THEREOF WHICH COMPRISES DISSOLVING IN SAID SOLUTION AT LEAST ONE METAL NITRATE SELECTED FROM THE GROUP CONSISTING OF THE NITRATED OF LITHIUM, CALCIUM,BIVALENT COPPER,ZINC AND TRIVALENT IRON, AND EXTRACTING URANYL RITRATE FROM SAID SOLUTION WITH A SELECTIVE SOLVENT IMMISCIBLE WITH SAID SOLUTION. 